The present invention relates to an unsaturated group-containing polycarboxylic acid resin, a resin composition comprising such a resin and suitable for a solder resist which can provide a permanent protective film of a printed circuit board excellent in heat resistance, chemical resistance and electric insulation property.
Ultraviolet curing compositions have recently been widely used for the purpose of saving resources and energy, improving the operability and productivity and the like. In the field of processing of printed circuit boards, various conventional inks such as solder resist ink and marking ink have also been changed from thermosetting compositions to ultraviolet curing compositions. Especially, solder resist ink has quickly changed to an ultraviolet curing composition from a conventional thermosetting composition.
Use of such an ultraviolet curing composition, however, is limited to the filed of what is called boards for public use which are used for radio, video, TV set and the like, and the application to the filed of what is called industrial boards which are used for computers, control machines and the like is not yet realized. This is because solder resist ink used for industrial boards is required to have a property such as a high electric insulating property, soldering resistance in a humid atmosphere and plating resistance, and the properties of the present solder resist ink for boards for public use have not reached the required level. With the recent tendency to smaller-sized and more highly-functioned electronic machines, industrial boards have been required to improve the pattern density of the circuit. Screen printing using conventional ultraviolet curing solder resist ink cannot produce satisfactory results due to the limitation of the printing accuracy. The conventional ultraviolet curing solder resist ink contains 1- to 3- functional monomer such as 2-hydroxyethyl methacrylate and trimethylolpropane triacrylate and various acrylate oligomers. During screen printing, these substances tend to bleed out, thereby disadvantageously obstructing soldering. To solve the above-described problems, for example, Japanese Patent Application Laid-Open (KOKAI) No. 60-208377 (1985) proposes a resin composition comprising a photopolymerizable epoxyvinyl ester resin, photopolymerization initiator and an amine epoxy hardener. Although this composition is excellent in heat resistance, adhesion, chemical resistance and electric insulation property, since an amine epoxy hardener is used, the storage stability is poor and an organic solvent must be used for developing images.
As a result of studies undertaken by the present inventors so as to solve these problems, the present inventors have found a resin composition which has a good storage stability, which is developable by an aqueous alkaline solution, which is excellent in heat resistance, adhesion, chemical resistance and electric insulation property and which is suitable for a solder resist. The present invention has been accomplished based on this finding.